This invention relates to a process for selectively removing protein aggregates from a protein solution. More particularly, this is invention relates to a process for selectively removing protein aggregates and virus from a protein solution.
Plasma derived protein solutions such as immunoglobulin protein (IgG,) and other proteins (natural or recombinant) such as monoclonal antibodies routinely contain protein aggregates comprising protein trimers or higher polymers. In order to administer this solution to a patient, it is necessary to first remove these aggregates to avoid a toxic response by the patient. When utilizing conventional filtration processes, aggregates are undesirable since the filter, especially the viral clearance filter, rapidly becomes plugged by the aggregates even at low aggregate concentrations of 0.01-0.1%. Accordingly, it has been necessary to utilize expensive gel chromatography or size exclusion chromatography processes to effect selective aggregate removal. Alternatively, one can use an ultrafiltration membrane operated in a constant diafiltration mode to effect aggregate removal, See U.S. Ser. No. 09/706,003, filed Nov. 3, 2000.
Viruses also are a potential contaminant in parenteral and other solutions containing a protein that is derived from either whole organisms or mammalian cell culture sources. Currently several chemical and physical methods exist to inactivate virus. These methods are not generic to all viruses equally and some operate at the expense of protein activity. For example, heat pasteurization is used in solutions where protein denaturization can be minimized through the addition of stabilizers. In the biotechnology industry, strategies have been adopted that combine several inactivation or removal steps in the downstream process to maximize virus removal capability and protein recovery. The operations used are generally those operations optimized to purify the parenteral product and are validated for the virus removal capability. Thus, virus removal is an additional capability from a by-product of normal operation. Finally, at the end of the process, steps such as chromatography, filtration or heat may be added to increase overall virus clearance. This strategy has two shortcomings; (1) the virus clearance of these operations may not apply to putative virus that cannot be assayed; and (2) the virus clearance of the process needs to be monitored continually. It is necessary to remove virus at a log retention value at least 3, i.e., at least about 99.9% removal.
Accordingly, it would be desirable to provide a process for removing protein aggregates from a protein solution by a filtration process that avoids premature plugging of the filtration device utilized in the process. In addition, it would be desirable to provide such a process that can be utilized in conjunction with a process for removing virus from the protein solution at a log retention value of at least 3.